Method and apparatus for random access in multicarrier wireless communications

ABSTRACT

Methods and apparatus for random access in multicarrier wireless communications are disclosed. Methods and apparatus are provided for physical random access channel (PRACH) resource signaling, PRACH resource handling, preamble and PRACH resource selection, random access response (RAR) reception, preamble retransmission, and transmission and reception of subsequent messages. A method for maintaining an allowed multicarrier uplink (UL) random access channel (RACH) configuration set by adding an UL carrier to the allowed RACH configuration set provided that a triggering event occurs and performing a random access (RA) procedure using the allowed RACH configuration set. A method for sending data in multicarrier wireless communications by determining a set of available UL carriers and selecting an UL carrier from the set of available UL carriers.

CROSS REFERENCE TO RELATED APPLICATIONS

This application continuation of U.S. patent application Ser. No.14/980,566 filed Dec. 28, 2015, which is a continuation of U.S. patentapplication Ser. No. 14/296,773 filed Jun. 5, 2014, which issued as U.S.Pat. No. 9,253,802 on Feb. 2, 2016, which is a continuation of U.S.patent application Ser. No. 12/766,677 filed Apr. 23, 2010, which issuedas U.S. Pat. No. 8,767,585 on Jul. 1, 2014, which claims the benefit ofU.S. Provisional Application No. 61/171,917 filed Apr. 23, 2009; U.S.Provisional Application No. 61/172,076 filed Apr. 23, 2009; U.S.Provisional Application No. 61/181,811 filed May 28, 2009; U.S.Provisional Application No. 61/293,366 filed Jan. 8, 2010; U.S.Provisional Application No. 61/303,937 filed Feb. 12, 2010; and U.S.Provisional Application No. 61/320,405 filed Apr. 2, 2010, the contentsof which are hereby incorporated by reference herein.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

In wireless communications a random access procedure may be used toassign dedicated radio resources to a wireless transmit/receive unit(WTRU). A dedicated radio resource may be, for example, a specificpreamble or physical random access channel (PRACH) resource. The randomaccess procedure may be either contention-free or contention-based, andmay include the following features: preamble transmission; random accessresponse (RAR) reception, in which the RAR contains a grant for anuplink (UL) transmission; transmission of message3 (msg3) forcontention-based random access; and contention resolution forcontention-based random access (for example, the WTRU may determinewhether the random access (RA) procedure was successfully completed).

FIG. 1 shows an example of a random access procedure including a WTRUand an evolved Node-B (eNB). The WTRU transmits a random accesspreamble. Then, the eNB responds with a RAR. Next, the WTRU may transmita scheduled transmission, for example, a msg3 transmission. Then, theeNB may perform contention resolution for contention-based random accessand the WTRU may determine whether the random access procedure wassuccessful.

A WTRU initiates a random access procedure when one of the followingevents occurs: initial access to the network when the WTRU has noestablished connection, that is from the radio resource control(RRC)_IDLE state; a RRC connection re-establishment procedure, randomaccess-physical downlink control channel (RA-PDCCH) order; handover;downlink (DL) data arrival during RRC_CONNECTED state requiring a randomaccess procedure; or UL data arrival during RRC_CONNECTED staterequiring a random access procedure, known as a random access schedulingrequest, (RA-SR).

In some wireless communications systems, such as, for example, Long TermEvolution (LTE), a WTRU may initiate a random access procedure due toone of the aforementioned events and a set of random access channel(RACH) resources is assumed to be available. The set of RACH resourcesis defined by a single index, prach-ConfigIndex, which may take a valuebetween 0 and 63 and identify a preamble format to be used, as well asthe set of subframes in which a preamble may be sent. The set ofsubframes may be further restricted by a provided physical random accesschannel (PRACH) mask index. In some systems, including orthogonalfrequency division multiple access (OFDMA) wireless communicationsystems, the WTRU operates in a single UL carrier. Thus, there is noambiguity as to which UL carrier may be used.

FIG. 2 shows a communication system 200 using a single UL carrier. TheWTRU 201 communicates with the network 203 using a single DL carrier205. A PRACH configuration is broadcasted on the DL carrier 205. TheWTRU sends a preamble using available PRACH resources provided by thesingle UL carrier 207.

The WTRU selects a RACH resource within the available set. This involvesthe selection of a random access preamble followed by the determinationof the next subframe containing an available RACH resource. The preambleis then transmitted in the next subframe (in the case of frequencydivision duplex (FDD)). In the case of time division duplex (TDD), thepreamble is transmitted in a randomly selected RACH resource within thenext subframe or the two subsequent subframes.

If a WTRU is configured to operate with multiple UL and DL carriers in aconnect mode, multiple RACH resources are available for use to initiatea random access procedure, if required. It may be beneficial to definerules under which a WTRU may determine a RACH resource to utilize andmay determine which sets of RACH resources may be considered availableamong the configured carriers.

SUMMARY

Methods and apparatus for random access in multicarrier wirelesscommunications are disclosed. Methods and apparatus are provided forPRACH resource signaling, PRACH resource handling, preamble and PRACHresource selection, RAR reception, preamble retransmission, andtransmission and reception of subsequent messages. A method formaintaining an allowed multicarrier UL RACH configuration set by addingan UL carrier to the allowed RACH configuration set provided that atriggering event occurs and performing a RA procedure using the allowedRACH configuration set. A method for sending data in multicarrierwireless communications by determining a set of available UL carriersand selecting an UL carrier from the set of available UL carriers. Amethod for initial RA transmission using a multicarrier UL RACH schemeby selecting an UL carrier from a plurality of UL carriers, selecting aRA preamble group based on the selected UL carrier, and selecting a RApreamble within the selected RA preamble group. A method fortransmitting a RAR using a multicarrier UL RACH scheme by determining aDL carrier for RAR transmission, computing a random access radio networktemporary identifier (RA-RNTI) associated with the RAR, and transmittingthe RAR including the RA-RNTI. A method for determining which DLcarrier(s) the RAR should be received on by monitoring at least onePDCCH in a common search space on at least one DL carrier for a RA-RNTIthat corresponds to the apparatus and receiving a RAR identified by theRA-RNTI. An apparatus configured to maintain an allowed multicarrier ULRACH configuration set by adding an UL carrier to the allowed RACHconfiguration set provided that a triggering event occurs and performinga RA procedure using the allowed RACH configuration set. An apparatusconfigured to perform multicarrier UL communications by determining aset of available UL carriers and selecting an UL carrier from the set ofavailable UL carriers.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an example of a random access procedure;

FIG. 2 is a block diagram of a single carrier communication system;

FIG. 3 shows an example LTE wireless communication system/accessnetwork;

FIG. 4 is a block diagram of an example LTE wireless communicationssystem;

FIG. 5 shows an example of RACH period reduction via staggering;

FIG. 6 shows a WTRU and network configured for use with multiple ULcarriers and DL carriers that may maintain an allowed RACH configurationset;

FIG. 7 is a flowchart of a procedure for adding a new PRACH/RACHconfiguration to the allowed RACH configuration set;

FIG. 8 is a flowchart of a procedure for removing or invalidating for aperiod of time a PRACH/RACH configuration from the allowed RACHconfiguration set;

FIG. 9 is a flowchart of an example procedure for invalidating aPRACH/RACH configuration from the allowed RACH configuration set for acertain period of time;

FIG. 10 is a flowchart of a procedure for determining that apredetermined maximum number of preamble transmissions have occurred andselecting a new random access resource or reporting a random accessproblem;

FIG. 11 is a flowchart of a procedure for selecting PRACH resources froma set of available PRACH resources;

FIG. 12 shows an example of transmission of simultaneous RACH requests;

FIG. 13 shows an example procedure for determining available ULcarriers;

FIG. 14 shows an example of a procedure demonstrating RA preambles groupB selection criteria;

FIG. 15 shows an example procedure of initial RA transmission;

FIG. 16 shows an example procedure of initial RA transmission;

FIG. 17 shows an example of a procedure for transmitting a Random AccessResponse (RAR) corresponding to a WTRU's preamble transmission;

FIG. 18 shows an overview of joint processing of a RACH request;

FIG. 19 shows an example of a procedure for determining which DL carrierthe RAR may be received on; and

FIG. 20 shows an example of a procedure for preamble retransmission.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIG. 3 shows a wireless communication system/access network 300 thatincludes an Evolved-Universal Terrestrial Radio Access Network (E-UTRAN)305, for example, 3GPP's Long Term Evolution (LTE). The E-UTRAN 305 mayinclude several evolved Node-Bs, (eNBs) 320. The WTRU 310 may be incommunication with an eNB 320. The eNBs 320 may interface with eachother using an X2 interface. Each of the eNBs 320 may interface with aMobility Management Entity (MME)/Serving GateWay (S-GW) 330 through anS1 interface. Although a single WTRU 310 and three eNBs 320 are shown inFIG. 3, it should be apparent that any combination of wireless and wireddevices may be included in the wireless communication system accessnetwork 300.

FIG. 4 is an example block diagram of an LTE wireless communicationsystem 400 including the WTRU 310, the eNB 320, and the MME/S-GW 330. Asshown in FIG. 4, the WTRU 310, the eNB 320 and the MME/S-GW 330 areconfigured to perform random access resource selection with multiplecarriers.

In addition to the components that may be found in a typical WTRU, theWTRU 310 includes a processor 416 with an optional linked memory 422, atleast one transceiver 414, an optional battery 420, and at least oneantenna 418. The processor 416 is configured to perform random accessresource selection with multiple carriers. The at least one transceiver414 is in communication with the processor 416 and the at least oneantenna 418 to facilitate the transmission and reception of wirelesscommunications. In case a battery 420 is used in the WTRU 310, it powersthe at least one transceiver 414 and the processor 416.

In addition to the components that may be found in a typical eNB, theeNB 320 includes a processor 417 with an optional linked memory 415,transceivers 419, and antennas 421. The processor 417 is configured toperform random access resource selection with multiple carriers. Thetransceivers 419 are in communication with the processor 417 andantennas 421 to facilitate the transmission and reception of wirelesscommunications. The eNB 320 is connected to the Mobility ManagementEntity/Serving GateWay (MME/S-GW) 330 which includes a processor 433with an optional linked memory 434.

In some wireless communications systems configured to perform uplinkmultiple-input multiple-output (MIMO) communications, such as, forexample, a system based on LTE Release 10 (R10) (also referred to as“LTE-Advanced” or “LTE-A”), a WTRU may be configured to use randomaccess resources on multiple configured UL carriers, that is, resourcesfrom more than one UL carrier. Additionally, a dedicated preamble may beassociated with a specific carrier. RACH resources may be selectedrandomly or in sequence where the RA procedure is initiated by themedium access control (MAC) layer. When random access resources areinitiated based on a PDCCH order, the PDCCH order and Random AccessResponse (RAR) may be transmitted on the DL carrier. The DL carrier maybe associated, for example, by the UL/DL pairing, or based onconfiguration of the uplink carrier supporting the RACH. The WTRU maydetermine that the UL communications have completely failed if the RAprocedure was initiated by MAC and the RA procedure was unsuccessful foreach of the RACH resources available to the WTRU in succession.

Some wireless communication systems, such as those based on LTE-A, mayinclude the use of bandwidth extensions such as carrier aggregation(CA). With CA, a WTRU may transmit and receive simultaneously overmultiple component carriers (CCs). Up to five CCs in the UL directionand in the DL direction may be available, thereby supporting flexiblebandwidth assignments up to 100 MHz. The WTRU may operate with multipleUL and DL carriers in the connected mode.

When referred to hereafter, the term “primary component carrier (PCC)”,or anchor carrier, may include a carrier of a WTRU configured to operatewith multiple component carriers for which some functionality (forexample, derivation of security parameters and non-access stratum (NAS)information) may be applicable to that particular CC. The WTRU may beconfigured with at least one PCC for the DL direction (DL PCC).Consequently, a carrier that is not a PCC of the WTRU may hereafter bereferred to as a “secondary component carrier” (SCC).

The DL PCC may, for example, correspond to the CC used by the WTRU toderive initial security parameters when initially accessing the system.The definition of the DL PCC may not be limited to this definition andmay be considered the CC that contains important parameters orinformation for system operation. A primary cell (PCell) may be the cellcorresponding to the combination of one DL PCC and one UL PCC. The PCellmay correspond to the DL CC used as anchor for NAS mobility and forderivation of security parameters (for example, during initial access).

PDCCH monitoring may be performed when a WTRU has an establishedconnection to the network. This PDDCH monitoring may occur when the WTRUis in RRC_CONNECTED state. A WTRU may perform PDCCH monitoring to getaccess to physical radio resources for DL assignment or UL granttransmissions.

A WTRU configured with multiple CCs may have to receive controlsignaling for scheduling of all CCs either on a single PDCCH (forexample, in the PCC) or on multiple PDCCHs, each on a different CC. Thismay result in an increase in the reception and processing of PDCCHsignaling. Decoding of the PDCCH channel may require the WTRU to performa number of blind decoding attempts, each validated by a cyclicredundancy check (CRC), to determine whether signaling may be intendedfor a specific WTRU. In addition, the network may use cross-carrierscheduling, where grants and/or assignments signaled on the PDCCH of oneCC may indicate transmissions on the physical uplink shared channel(PUSCH) or physical downlink shared channel (PDSCH) corresponding to adifferent CC. Blind decoding complexity may be reduced by requiring aWTRU to monitor control signaling only on a subset of the configuredCCs. A specified PDCCH monitoring set may represent a set of CCs onwhich the WTRU may be required to monitor, the size of which may be lessthan or equal to the size of the UL/DL CC set and may comprise only CCsthat are in the WTRU DL CC set.

As used herein, the terms “PRACH configuration” and “RACH configuration”refer to a set of parameters corresponding to the information elements(IEs). Examples of PRACH/RACH configuration parameters include the IEs'PRACH-Config and RACH-ConfigCommon as used in, for example, Release 8 ofLTE. A PRACH/RACH configuration may apply to a specific pair of DL andUL carriers. The DL carrier of a PRACH or a RACH configuration is acarrier on which these configurations may be broadcasted. The UL carrierof a PRACH or a RACH configuration is the carrier on which the preamblemay be transmitted. The UL carrier may be obtained from the defaultduplex distance or may be signaled explicitly from the DL carrier, forexample, in system information block 2 (SIB2).

The number of aggregated carriers in the UL and DL directions may bedesignated, respectively, by N_(UL) and N_(DL). In asymmetric carrieraggregation, N_(UL) may not equal N_(DL). The RACH period of each UL CCmay be denoted as T_(RACH).

The RACH period may be reduced from a WTRU's perspective via staggering.For example, the RACH period of each UL CC may remain at 10 ms while therandom access opportunity timing may be staggered across aggregated ULCCs. For example, one UL CC may have no timing offset while another ULCC may have a timing offset of 5 ms. From the WTRU's perspective, theRACH period may appear to be 5 ms, resulting in a 5 ms “effective RACHperiod.” Thus, different UL CCs may have a different RACH timing offset(subframe) within the same RACH period. An effective RACH period of lessthan 10 ms (the LTE RACH period) may be achieved.

FIG. 5 shows an example of RACH period reduction via staggering 500,including a first UL carrier (UL carrier 1) 502 and a second UL carrier(UL carrier 2) 504. UL carrier 1 502 has a 10 ms RACH period. UL carrier2 504 has a 10 ms RACH period with a timing offset of 5 ms from ULcarrier 1 502. Thus, FIG. 5 demonstrates a 5 ms effective RACH period.Generally, an effective RACH period of T_(RACH)/N_(UL) may be achieved.

FIG. 6 shows a WTRU 602 and network 604 configured for use with multipleUL carriers 606 and DL carriers 608 that may maintain a set of RACHconfigurations that may potentially be used by the WTRU 602 for randomaccess. This set may be referred to as the “allowed RACH configurationset.” An element of the allowed RACH configuration set may include aPRACH configuration or may include a PRACH configuration and a RACHconfiguration. A WTRU configured for UL MIMO may require the followinginformation in order to perform a RA procedure: RACH parameters for eachUL carrier on which the WTRU may transmit RACH messages (for example, ascarried in SIB2 in LTE); RACH start timing offset of each UL carrier onwhich the WTRU may transmit RACH messages; and location (for example,center frequency) and the bandwidth of each UL carrier on which the WTRUmay transmit RACH messages. A WTRU may only need to acquire thisinformation when the WTRU transitions from idle to connected state. AWTRU transitioning from dormant to active sub-state may already knowsuch information.

In one embodiment, a WTRU may determine the allowed RACH configurationset via information received on a DL PCC using one or a combination offields. The fields may include: the spare (or reserved) bit in P-BCH;the nonCriticalExtension field of SIB1; or a new SIB type that maycomplement SIB2. This embodiment may also include transmitting SIB2 foreach DL carrier that is mapped to or paired with each UL carrier onwhich the WTRU may perform a RA procedure. Optionally, the commoninformation between different SIBs may be transmitted or signaled once.

In another embodiment, a WTRU may determine the allowed RACHconfiguration set via SIB2, which may be transmitted on each DL PCC.SIB2 may contain RACH configuration parameters and an UL carrier'slocation and bandwidth. Each DL carrier may use a predetermined numberof bits to signal a RACH start timing offset of the UL CC that the DLcarrier is mapped to or paired with. One or a combination of severalfields may be used to accomplish this, including the spare (or reserved)bit in the physical broadcast channel (PBCH); the nonCriticalExtensionfield of SIB1; or a new SIB type. This embodiment may be applied to ascenario in which a WTRU transitions from dormant to active sub-state.Optionally, the RACH start timing offset is transmitted on the DL PCC.

In another embodiment, a WTRU may determine the allowed RACHconfiguration set implicitly through the WTRU carrier configurationprovided, for example, by RRC messaging or signaling. The allowed RACHconfiguration set may be chosen as one or a plurality of the followingsets. One possible set may include all PRACH/RACH configurationsbroadcasted by the DL carriers that the WTRU is configured to use.Another possible set may include one PRACH/RACH configuration per ULcarrier that the WTRU is configured to use. The PRACH/RACH configurationfor each UL carrier may be provided by its corresponding DL carrier ormay be provided by dedicated signaling. Another possible set may includeat most one PRACH/RACH configuration per UL carrier that the WTRU isconfigured to use, provided that a single PRACH/RACH configurationexists for each set of UL carriers sharing a particular timing alignment(TA). Timing alignment may also include “timing advance,” which may be avalue that represents how early a WTRU may start its transmission in agiven subframe as compared to its DL reception. Timing advance may be afunction of the WTRU's distance to the eNB or may be a function of thefrequency band. Another possible set may include one or more PRACH/RACHconfigurations per UL carrier associated with one or more DL carriersincluded in the PDCCH monitoring set.

Each of the N_(DL) DL carriers may be used by distinct cellsbroadcasting their own cell identities. The WTRU may acquire systeminformation pertaining to one or a plurality of DL carriers. The systeminformation may be transmitted on a carrier (for example, a DL PCC), ona subset of specific carriers, or on all DL carriers.

A WTRU may modify the allowed RACH configuration set according to eventsor upon receiving explicit signaling indicating that the allowed RACHconfiguration set should be modified. A WTRU may add a new PRACH/RACHconfiguration set to the allowed RACH configuration.

FIG. 7 is a flowchart of a procedure 700 for adding a new PRACH/RACHconfiguration to the allowed RACH configuration set. A WTRU may add anew PRACH/RACH configuration to the allowed RACH configuration setprovided that at least one of a plurality of addition triggering eventsoccurs. For example, a WTRU may maintain an allowed RACH configurationset 702. If an addition triggering event occurs 704, the WTRU maydetermine whether to add a new PRACH/RACH configuration to the allowedRACH configuration set 706. The WTRU then adds a PRACH/RACHconfiguration to the allowed RACH configuration set 708. The WTRU mayperform a RA procedure 710. An addition triggering event may also beused as any type of triggering event, such as a removal or invalidationtriggering event.

An addition triggering event may include receiving explicit signalingfrom the network. The explicit signaling may include an indicator sentalong with the carrier configuration via RRC signaling. The RRCsignaling may indicate that the PRACH/RACH configuration broadcasted onthe DL carrier being added to the configuration should be added to theallowed RACH configuration set.

Alternatively or additionally, an addition triggering event may includereceiving a PDCCH order on the DL carrier broadcasting the PRACH/RACHconfiguration. Alternatively or additionally, an addition triggeringevent may include receiving a PDCCH order with a carrier indicationfield (CIF) indicating the DL carrier broadcasting the PRACH/RACHconfiguration. Alternatively or additionally, an addition triggeringevent may include receiving a PDCCH order with a CIF indicating the DLcarrier that is broadcasting the PRACH/RACH configuration. A PDCCH ordermay be control signaling received from the network instructing the WTRUto initiate a RA procedure using the RACH parameters provided in thecontrol signaling, assuming they are present. The PDCCH order mayindicate the CC for which the control signaling is applicable or theidentity of the DL CC on which the WTRU may read the broadcastedconfiguration.

FIG. 8 is a flowchart of a procedure 800 for removing or invalidatingfor a period of time a PRACH/RACH configuration from the allowed RACHconfiguration set. A WTRU may remove or invalidate a PRACH/RACHconfiguration from the allowed RACH configuration set on a conditionthat at least one of a plurality of removal/invalidation triggeringevents occurs. In the procedure 800 of FIG. 8, a WTRU may maintain anallowed RACH configuration set 802. If a removal/invalidation triggeringevent occurs 804, the WTRU may determine whether to remove or invalidatea PRACH/RACH configuration from the allowed RACH configuration set 806.The WTRU may remove or invalidate a PRACH/RACH configuration from theallowed RACH configuration set 808. The WTRU may perform a RA procedure810. A removal/invalidation triggering event may also be used as anytype of triggering event, such as an addition or invalidation triggeringevent.

A removal/invalidation triggering event may include receiving explicitsignaling from the network. Examples of explicit signals include RRC,MAC, or PDCCH signals that may be similar to a backoff indicator. Abackoff indicator may be an indication that the WTRU may refrain fromperforming a given procedure, at least for a certain period of time.Alternatively or additionally, a removal/invalidation triggering eventmay include determining that the DL carrier broadcasting the PRACH/RACHconfiguration has been removed from the carrier configuration. Anexample may be receiving a RRC reconfiguration message. Alternatively oradditionally, a removal/invalidation triggering event may includedetermining that the UL carrier corresponding to the PRACH/RACHconfiguration has been removed from the carrier configuration. Anexample may be receiving a RRC reconfiguration message. Alternatively oradditionally, a removal/invalidation triggering event may includereaching the maximum number of preamble transmissions (for example,preambleTransMAX) after transmitting a preamble for a PRACH/RACHconfiguration. Another example may include an unsuccessful RARreception, where preambleTransMAX is equal to the maximum value. Forexample, upon reaching the maximum value, the WTRU may remove orinvalidate the corresponding configuration, in addition to otherresponses the WTRU may already perform upon reaching the maximum value.

FIG. 9 is a flowchart of an example procedure 900 for invalidating aPRACH/RACH configuration from the allowed RACH configuration set for acertain period of time. A WTRU that receives explicit signaling from thenetwork 904 may invalidate a PRACH/RACH configuration from the set for aperiod of time 906. For example, the signaling may be similar to abackoff indicator or may be a backoff or prohibit time during which theWTRU may not use a specific PRACH/RACH configuration. Optionally, theWTRU may use a different resource on a different CC 908. An invalidationtriggering event may also be used as any type of triggering event, suchas an addition or removal/invalidation triggering event.

The criterion for indicating a “random access problem” may be modifiedbased on the allowed RACH configuration set so that a WTRU may attemptrandom access on multiple UL carriers.

FIG. 10 is a flowchart of a procedure 1000 for determining that apredetermined maximum number of preamble transmissions have occurred andfor selecting a new random access resource or for reporting a randomaccess problem. If the preamble transmission counter exceeds the maximumnumber of preamble transmissions 1004 (for example,PREAMABLE_TRANSMISSION_COUNTER=preambleTransMax+1), a WTRU may remove orinvalidate the PRACH/RACH configuration from the allowed RACHconfiguration set 1006. Optionally, the WTRU may remove or invalidatePRACH/RACH configurations in the following cases: (1) the configurationwas provided by dedicated signaling, for example, via RRC configuration;(2) the configuration was provided for a SCC of the WTRU's configurationor for all SCCs of the same frequency band; or (3) the configuration wasconfigured such that, upon failure of the RA procedure on thecorresponding resource, the WTRU does not trigger radio link failure(RLF).

Alternatively or additionally, the WTRU may remove or invalidate the DLand/or UL carrier corresponding to the PRACH/RACH configuration used fortransmission of the preamble from the carrier configuration 1008. Thismay also result in the WTRU removing the PRACH/RACH configuration fromthe allowed RACH configuration set 1006. The WTRU may then determinewhether there is at least one PRACH/RACH configuration in the allowedRACH configuration set 1010.

If the WTRU determines that there is at least one valid PRACH/RACHconfiguration in the allowed RACH configuration set, the WTRU may resetthe preamble transmission counter to 1 (for examplePREAMABLE_TRANSMISSION_COUNTER=1) 1012. The WTRU may then proceed toselection of a random access resource within the allowed RACHconfiguration set 1016 and may optionally set the backoff parametervalue to 0 ms and flush the msg3 buffer 1014.

If the WTRU determines that there is not at least one PRACH/RACHconfiguration in the allowed RACH configuration set (meaning the allowedRACH configuration set is empty or there is no valid item in the set),the WTRU may indicate a random access problem to upper layers 1018.Examples of the indication in element 1018 may include “RA problems” or“UL RLF.” Optionally, this may be time-limited. For example, given thatthe indication pertains to the management of the resources available tothe WTRU, the indication may be provided or may be valid only for acertain amount of time. The amount of time may be based on a timer ormay be based on the subsequent addition of an item to the allowed RACHconfiguration set. The maximum number of preamble retransmissions for agiven PRACH resource, whether dedicated or not, may or may not be thesame for all resources of the WTRU's allowed RACH configuration set. Forexample, the parameter corresponding to the maximum number of preambleretransmissions may be common to all items in the allowed RACHconfiguration set or may be specified for each item or for particulargroups in the allowed RACH configuration set.

As an example, in one possible embodiment, a WTRU may attempt a RAprocedure using a first PRACH/RACH configuration for which a failure ofthe RA attempt does not trigger a RLF (for example, a RA attempt in aSCC for gaining TA and/or a RA attempt triggered by a PDCCH orderreceived from the network). Additionally, the WTRU may determine that aRLF may not be triggered by a failure based on at least one of thefollowing: (1) the PRACH/RACH configuration was received via dedicatedsignaling; (2) the PRACH/RACH configuration corresponds to a SCC of theWTRU's configuration; or (3) the PRACH/RACH configuration indicates thatRA failure does not trigger a RLF.

If a failure of the RA procedure is detected for the first PRACH/RACHconfiguration, the WTRU may perform a RA procedure using a secondPRACH/RACH configuration for which a failure of the RA attempt doestrigger a RLF and for which the WTRU determines that a RLF shall not betriggered upon failure based on at least one of the following: (1) thePRACH/RACH configuration was received by signaling from the broadcastedsystem information; (2) the PRACH/RACH configuration corresponds to aPCC of the WTRU's configuration; or (3) the PRACH/RACH configurationindicates that RA failure triggers a RLF. If the failure of the RAprocedure is detected for the second PRACH/RACH configuration, the WTRUmay indicate a “random access problem” to upper layers via, for example,RRC messaging.

The WTRU may receive a network request to perform a random accessprocedure. This request may be signaled on the PDDCH (hereinafter “PDCCHRA order”), for example, using downlink control information (DCI) format1a. For a WTRU configured to operate with multiple CCs and possibly alsowith cross-carrier scheduling (for example, where the PDCCH in onecarrier may be used to schedule assignments on the PDSCH or grantresources on the PUSCH of a different carrier), it may be necessary todetermine which RACH resource the WTRU may use upon reception of a PDCCHRA order.

RACH resource selection may include selection of a PRACH among a set ofavailable PRACHs and selection of a preamble. The selection of a PRACHmay include choosing PRACHs that may be on different UL carriers. Theselection of a preamble may include choosing a preamble from a preamblegroup on a condition that more than one preamble group exists.

To determine which resource the WTRU may select for the RA procedure,the WTRU may make a selection at least in part as a function of the CCfor which the received control information is applicable, on a conditionthat the WTRU receives a request from the network to perform randomaccess. For example, the selected resource may correspond to a PCC or aSCC of the WTRU's allowed RACH configuration set.

A WTRU may detect control information on the PDCCH. For example, theWTRU may receive a DCI format scrambled with a radio network temporaryidentifier (RNTI) applicable to the WTRU (WTRU's Cell-RNTI (C-RNTI)).Upon successful detection of control information on the PDCCH indicatingthat the WTRU may perform the random access procedure, a WTRU may detectwhether the DCI format is applicable to a SCC of the WTRU'sconfiguration or to a PCC of the WTRU's configuration. A DCI format maybe considered to be applicable to a CC provided that: (1) it is receivedon the PDCCH of the DL CC corresponding to the CC; or (2) the CIFindicates the CC or corresponds to the CC. If the DCI format isapplicable to a SCC, the WTRU may perform at least one or a combinationof the following: (1) The WTRU may refrain from performing a randomaccess attempt. For example, the WTRU may ignore the received PDCCH RAorder. This may be on a condition that a WTRU only considers a PDCCHorder received in a PCC as valid; otherwise, it may be a false detectionor a network error. For example, a false detection may be that a WTRUsuccessfully decodes a DCI message scrambled on the PDCCH using one ofthe WTRU's RNTI, but the message was not intended for that particularWTRU. Decoding may use some form of checksum verification using a 16-bitRNTI, so false detection may occur. (2) The WTRU may perform a RAprocedure in a PCC of its configuration, which may be the case if a WTRUmay only perform RA in a PCC (for example, where there is DL dataarrival for an unsynchronized WTRU). (3) The WTRU may perform a RAprocedure using a RACH resource of the applicable SCC, which may be thecase if a WTRU performs RA in a SCC (for example, for gaining TA for theCC or a group of CCs with the same TA requirement and/or in the case ofdownlink data arrival for an unsynchronized WTRU). (4) The WTRU mayperform a RA procedure using a RACH resource of any CC which may be partof a group for which the corresponding UL CC has the same TArequirement, which may be the case if different UL CCs may havedifferent TA requirements. (5) The WTRU may perform a RA procedure usinga resource indicated in the DCI message, for example, using an index toa resource which is part of the WTRU configuration. This may be usefulfor load balancing in the case of downlink data arrival for anunsynchronized WTRU.

If the DCI format is applicable to a PCC, the WTRU may perform a RAprocedure on a resource of the PCC. A DCI format may be considered to beapplicable to a CC on a condition that (1) it is received on the PDCCHof the DL CC corresponding to the CC; or (2) the CIF indicates the CC orcorresponds to the CC.

A WTRU may determine which set or sets of PRACH configurations withinthe allowed RACH configuration set are available for selection of aPRACH resource. The selection of the PRACH resource may optionally alsobe considered to be at least partly a function of the reason and/orcause for which the WTRU performs a random access procedure. Forexample, the reason or cause may be a PDCCH RA order (with or withoutCIF), RA-SR, or RA for a connection re-establishment. The set of PRACHresources that the WTRU may consider as available may depend on whattriggered the random access procedure and how the random accessprocedure was triggered. The following embodiments are examples of waysin which a WTRU may select a PRACH resource from a set of availablePRACHs.

In one embodiment, a CIF may be used in a PDCCH containing a PDCCH orderfor a RA procedure. The CIF may indicate at least one DL CC and/or atleast one UL CC. The WTRU may receive a PDCCH order along with a CIF andselect a PRACH from a set of available PRACH resources given by thePRACH configuration (for example, prach-ConfigIndex) broadcasted on theDL carrier indicated by the CIF. This indication may be an explicitindication of the PRACH configuration or may be implicit, for example,based on association with a paired UL carrier.

Alternatively or additionally, the WTRU may select a PRACH resource froma set of PRACHs available on the UL carrier indicated by the CIF. Thisindication may be an explicit indication of the PRACH configuration ormay be implicit, for example, based on association with a paired DLcarrier. The set of PRACHs may include the union of multiple sets ofPRACHs, with the sets provided via the broadcasts of PRACHconfigurations on multiple DL carriers, on a condition that more thanone DL carrier broadcasts PRACH configurations for the same UL carrier.

Alternatively or additionally, the WTRU may select a PRACH resource froma set of available PRACH resources represented as an indexed set andusing the CIF as an index. The CIF may be interpreted as an index to anordered sequence of a set of PRACH resources. The order of the set ofPRACH resources in the index may be the order in the WTRU'sconfiguration of the DL carriers on which the set of PRACH resources wasbroadcasted.

In another embodiment, the WTRU may receive a PDCCH order, with orwithout a CIF, or may initiate a RA procedure due to a SR beingtriggered without a valid PUCCH resource. A SR may be triggered if aWTRU needs to send a Buffer Status Report (BSR). A BSR may be triggeredperiodically, if configured, or if the WTRU has new data available forUL transmission with a higher priority than any existing data. The WTRUmay select a PRACH resource from a set of available PRACH resourcesprovided by the PRACH configuration broadcasted by the DL carriercorresponding to the PCell, on a condition that the PRACH configurationis present in the allowed RACH configuration set. Otherwise, the WTRUmay determine that the set of available PRACH resources is provided bythe union of all sets of PRACH resources provided by all PRACHconfigurations in the allowed RACH configuration set.

Alternatively or additionally, the WTRU may select a PRACH resource froma set of available PRACH resources provided by the sets of PRACHsavailable on the UL carriers for which the applicable TA timer lastexpired or for which the last TA command was received.

Alternatively or additionally, the WTRU may use an identity of the WTRUin the selection of the PRACH resource from the set of available PRACHresources. For example, this may include using a hashing function orusing the identity as an index to a list, for example, to distribute theload across available resources. PRACH resources may be available tomultiple WTRUs and access to the PRACH resources may becontention-based. Thus, it may be useful to distribute the load as thenumber of WTRUs in a cell increases. A hash function may randomize theselection of one resource from a set of resources, which may allow eachresource an equal chance of being selected. This may help distribute theload across available resources.

Alternatively or additionally, the WTRU may consider the set ofavailable resources as a priority list. For example, a resource may havea higher priority based on at least one of: (1) a configuration of thenetwork; (2) the DL path loss, based on measurements for a DL CC usedfor the path loss determination for the UL CC corresponding to theresource; (3) a ranking of the resource based on some criteria, forexample, the maximum number of attempts before the WTRU may declare RAfailure; (4) round-robin attempts; (5) previous outcome of a RACHprocedure on the resource; (6) whether the CC is a PCC or a SCC of theWTRU's configuration; (7) whether or not the resource was provided tothe WTRU in a dedicated manner (for example, by dedicated RRC signalingthat configured the WTRU for multicarrier operation), possibly having aspecific number of preamble transmissions for the resource that differsfrom that of the maximum number of preamble transmissions broadcasted onthe DL CC corresponding to that resource; or (8) whether or not theresource was provided to the WTRU via broadcasted system information(for example, by RRC signaling received by the WTRU on the BCCH, whichmay include the maximum number of preamble transmissions).

As an example, the WTRU may give a higher priority to a resourceprovided in a dedicated manner (such as, a resource corresponding to aSCC of the WTRU's configuration). If the random access procedure failson such a resource (meaning that the procedure is not successful afterreaching the maximum number of preamble transmissions), the WTRU mayselect a resource provided by system information (for example, aresource corresponding to a PCC of the WTRU's configuration). The WTRUmay then attempt a random access using this resource (for example, ifthe WTRU does not declare UL RLF due to a RACH failure using thededicated resource). On a condition that the random access attempt failsfor the resource provided by system information, the WTRU may declare ULRLF and may perform recovery actions accordingly.

In another embodiment, the WTRU may receive a PDCCH order, with orwithout a CIF. The WTRU may select a PRACH resource from a set ofavailable PRACHs determined as the union of the sets of PRACHs providedby all PRACH configurations in the allowed RACH configuration set, on acondition that the PDCCH order indicates that the preamble may be chosenrandomly (for example, preamble index=“000000”). Otherwise, the set ofavailable PRACHs may be selected according to any of the otherembodiments described herein.

Alternatively or additionally, the WTRU may select a PRACH resource froma set of available PRACHs determined as the union of the sets of PRACHsprovided by PRACH configurations in the allowed RACH configuration setfor which the corresponding UL carrier is not synchronized (or nottime-aligned).

In another embodiment, the WTRU may initiate a random access procedureupon receiving an UL grant for a PUSCH on an UL carrier for which theapplicable TA timer has expired. The WTRU may select a PRACH resourcefrom the set of available PRACHs provided by the sets of PRACHsavailable on the UL carrier for which the applicable TA timer hasexpired. Alternatively or additionally, the WTRU may select a PRACHresource from the set of available PRACHs provided by the sets of PRACHsavailable on the UL carrier for which the applicable TA timer hasexpired as well as any UL carrier sharing the same TA (for example, inthe same TA subgroup).

FIG. 11 is a flowchart of a procedure 1100 for selecting PRACH resourcesfrom a set of available PRACH resources defined by multipleprach-ConfigIndex messages. Optionally, a WTRU may determine whether thetransmission is the initial preamble transmission 1104, for example, ifthe parameter PREAMBLE_TRANSMISSION_COUNTER is equal to 1 and/or if themsg3 buffer is empty. If the transmission is not the initial preambletransmission (for example, PREAMBLE_TRANSMISSION_COUNTER is greater than1), the WTRU may optionally be constrained to select a PRACH resourcewithin the set indicated by the same prach-ConfigIndex utilized for theinitial preamble transmission 1106.

The WTRU may select a PRACH resource from a set of available PRACHresources 1108. Optionally, the WTRU may select a PRACH resource on acondition that the transmission is the initial preamble transmission1104. One or a combination of the following four embodiments may be usedto select a PRACH resource from a set of available PRACH resources.

In one embodiment, a WTRU may select resources corresponding to aspecific prach-ConfigIndex within the available set. Optionally, thisselection may be determined randomly. The WTRU may then determine thenext available subframe containing a PRACH resource for this specificprach-ConfigIndex. Optionally, other restrictions may be applied. Forexample, using TDD mode in LTE, the WTRU may randomly select oneoccasion within three consecutive occasions. The occasions may startfrom the first available occasion or may start no earlier than at n+6subframes provided that a PDCCH order is received at subframe n.

In another embodiment, a WTRU may determine the next available subframecontaining an available PRACH resource within the set of all availablePRACH resources given by the set of prach-ConfigIndex parameters thatmay indicate resources on more than one UL frequency. The WTRU may thenselect one available PRACH resource within the subframe (or within thenext n subframes), on a condition that there is more than one PRACHresource available. The selection may be random. Another way to describethis embodiment is that a WTRU may select the PRACH configuration(s) orprach-ConfigIndex for which it can utilize a PRACH resource the earliestamong the available PRACH resources.

In another embodiment, the WTRU may select a resource from a set ofavailable PRACH resources with a further restriction that the selectedPRACH resource corresponds to a UL CC for which the associated DL CC isconfigured and activated. For example, the WTRU may receive a PDSCHtransmission and may also monitor the PDCCH. This may also correspondonly to a DL CC that has been explicitly activated by signaling receivedfrom the network. This may be useful to determine the initial transmitpower of the preamble, which may be a function of the path loss measuredfrom a DL CC used for the path loss determination for the UL CC.

In another embodiment, the WTRU may select a resource from a set ofavailable PRACH resources with a further restriction that the selectedresource corresponds to a UL CC that is configured, for example, meaningthat the UL CC is available to the WTRU for UL transmissions.Optionally, the UL CC may also need to be activated, assuming that anactivated/deactivated state is applicable to UL CCs. This may onlycorrespond to an UL CC that has been explicitly activated by signalingreceived from the network.

Alternatively or additionally, for any of the above-describedembodiments, the WTRU may select any PRACH resource within multipleprach-ConfigIndex messages if the PRACH resources are on the same ULcarrier as the UL carrier used for the initial preamble transmission.

Referring again to FIG. 11, upon selecting a PRACH resource 1108, theWTRU may select RACH parameters (for example, preambleInfo,powerRampingparameters and ra-SupervisionInfo) according to the RACHconfiguration broadcasted from the same DL carrier that had broadcastedthe PRACH configuration from which the PRACH resource used for theinitial preamble transmission was chosen 1110. Alternatively oradditionally, the WTRU may be provided with a fixed (noncarrier-dependent) set of RACH parameters 1112. This set of RACHparameters may be implicitly determined from the DL carriercorresponding to the PCell 1114 or may be obtained via dedicatedsignaling 1116.

Upon selecting a PRACH resource from the set of available PRACHs asdescribed above, a WTRU may select a preamble. The WTRU may select apreamble according to the manner in which the WTRU selected a PRACHresource.

If the WTRU selected PRACH resources corresponding to a specificprach-ConfigIndex within the allowed set, the WTRU may select a preambleusing RACH parameters in preambleInfo from the RACH configurationbroadcasted on the same DL carrier that broadcasted the selected PRACHconfiguration, for example, as in LTE Release 8.

If a dedicated preamble is provided by the network, the WTRU may selecta preamble using RACH parameters in preambleInfo from the RACHconfiguration broadcasted on the same DL carrier that broadcasted theselected PRACH configuration, for example, as in LTE Release 8.

If the WTRU selected the PRACH configuration(s) or prach-ConfigIndex forwhich it can utilize a PRACH resource earliest among the available PRACHresources, the WTRU may select a preamble after the PRACH resources aredetermined. Optionally, the WTRU may then use the RACH parameters inpreambleInfo from the RACH configuration broadcasted on the same DLcarrier that broadcasted the PRACH configuration from which the PRACHresource was selected.

Alternatively or additionally, the WTRU may select a preamble in advancebased on a preambleInfo set of parameters that may be provided by thenetwork in a dedicated manner. Alternatively or additionally, the WTRUmay select the preambleInfo set of parameters, among the set of DLcarriers broadcasting the available PRACH resources, for whichnumberOfRA-Preambles is the smallest.

Employing carrier aggregation in wireless communications may allow theRACH delay to be reduced via simultaneous transmission of multiplerandom access preambles within a given RACH period. A WTRU may sendsimultaneous random access preambles on multiple or all of the N_(UL)CCs. The transmitted preambles may be the same or may be different. Thismay reduce delay if there is contention on the UL channel or heavy DLtraffic because other CCs may be in a better position to provide PUSCHresources for a msg3 transmission.

FIG. 12 shows an example of transmission of simultaneous RACH requests1200, including a first UL carrier (UL carrier 1) 1202 and a second ULcarrier (UL carrier 2) 1204. A random access preamble is sent on ULCarrier 1 1202 and UL Carrier 2 1202 simultaneously. At least one of thesent preambles may be detected. An eNB may send back one random accessresponse (RAR).

FIG. 13 shows an example procedure 1300 for determining available ULcarriers. A WTRU may have UL data to send 1304 and may need to determineavailable UL carriers 1306. If the number of UL carriers, N_(UL), is notgreater than 1 1308, the WTRU may select, if possible, the one ULcarrier that is available 1310. If N_(UL) is greater than 1 1308, theWTRU may randomly select an UL carrier 1312 within the configured set ofUL CCs (for example, PRACH resources). As an example, the WTRU mayperform the selection using a uniform probability mass function or anarbitrary probability mass function. An arbitrary probability massfunction may be signaled from the system information acquired on the DLcarrier(s) or may be derived from UL load information broadcasted on theDL carrier(s).

Alternatively, if the number of UL carriers, N_(UL), is greater than 11308, the WTRU may select an UL carrier based on estimated path loss1314 to the eNB. For example, if there are two UL carriers, the WTRU mayselect a first UL carrier on a condition that the path loss is below apredetermined threshold and a second UL carrier on a condition that thepath loss is above the predetermined threshold. Generally, a set ofN_(UL)−1 thresholds (T_(i)) may be used for N_(UL) UL carriers, where ULcarrier #i may be selected if T_((i−1))<path loss <T_(i). Thefrequencies of the UL carriers may not need to increase with i. Thethresholds T₁ used for comparison may depend on the preamble group(which is also dependent on the path loss), thus possibly providing afiner granularity of path loss information. Alternatively, thethresholds used for the preamble group determination may be dependent onthe choice of the UL carrier. The thresholds may be signaled as part ofsystem information.

If the different DL and UL carriers are in different frequency bands,there may be a significant difference of path loss between the carriersthat are in different bands. To address this difference, the path lossmay be measured on a specific DL carrier (or any DL carrier on aspecific frequency band) that is signaled by system information. Second,the path loss may be measured on any DL carrier. The WTRU may apply acompensation offset or factor to the path loss estimate, which maydepend on the frequency band. The offset may be pre-defined or may besignaled from system information.

Alternatively, if the number of UL carriers, N_(UL), is greater than 11308, the WTRU may select a UL carrier based on the difference betweenthe estimated path loss to the serving cell (for example, an eNB) andthe estimated path loss to a neighboring cell 1316. The neighboring eNBor cell may be the next strongest eNB or cell, or may be signaled fromsystem information. For example, on a condition that there are two ULcarriers, the WTRU may select one UL carrier on a condition that thepath loss difference is below a predetermined threshold and the other ULcarrier on a condition that the path loss difference is above thethreshold. Generally, a set of N_(UL)−1 thresholds T_(i) may be used inthe case of N_(UL) UL carriers, where UL carrier #i is selected ifT_((i−1))<path loss difference <T_(i). The frequencies of the ULcarriers may not need to increase with i. This may allow the WTRU toquickly indicate to the network whether some resource blocks used insome neighboring cells may be used or may not be used for the accessingthe WTRU while considering interference.

A WTRU may select RA preambles group A or RA preambles group B forpreamble transmission based on certain criteria. RA preambles group Amay be a group that is already configured. RA preambles group B, ifavailable, may be used to indicate to the network that the WTRU has amessage larger than a given value or may indicate that the WTRU ispower-limited. This may enable the eNB to provide a grant based on theWTRU's location or distance within a cell. FIG. 14 shows an example of aprocedure 1400 demonstrating RA preambles group B selection criteria. RApreambles group B may be selected provided that: (1) RA preambles groupB exists; (2) potential message size is greater thanMESSAGE_SIZE_GROUP_A; and (3) path loss (L) meets the inequality:

L<Pmax−PREAMBLE_INITIAL_RECEIVED_TARGET_POWER−DELTA_PREAMBLE_MSG3−messagePowerOffsetGroupB  (Equation 1)

The potential message size may be data available for transmission plusan AMC header and, where required, MAC control elements. If the abovecriteria are not met, RA preambles group A may be selected.

Referring to FIG. 14, if RA preambles group B does not exist 1402, RApreambles group A is selected 1404. If RA preambles group B does exist1402, but potential message size is not greater thanMESSAGE_SIZE_GROUP_A 1406, RA preambles group A is selected 1404. If RApreambles group B does exist 1402 and the potential message size isgreater than MESSAGE_SIZE_GROUP_A 1406, but path loss is not less thanthe quantity defined by Equation 1 1408, RA preambles group A isselected 1404. If RA preambles group B does exist 1402, the potentialmessage size is greater than MESSAGE_SIZE_GROUP_A 1406, and path loss isless the quantity defined by Equation 1 1408, RA preambles group B isselected step 1410.

Using the defined RA preambles group B criteria, a WTRU may use one or acombination of the following embodiments to select a RA preamble amongmultiple UL CCs available for RA. FIG. 15 shows an example procedure1500 of initial RA transmission. The WTRU may divide UL CCs availablefor random access into two carrier sets 1502. Carrier Set A may includecarriers in which RA preambles group B criteria are not met 1504.Carrier Set B may include carriers in which RA preambles group Bcriteria are met 1506. On a condition that Set B is empty 1508, one ULcarrier within Carrier Set A may be selected 1510. On a condition thatSet B is non-empty 1508, one UL carrier within Carrier Set B may beselected 1512. The WTRU may then select an UL CC within the chosen setin one or a plurality of ways. The WTRU may randomly select one ULcarrier within the carrier set 1514. Alternatively, the WTRU may selectthe UL carrier with the smallest path loss within the carrier set 1516.Alternatively, if Pmax is assigned per UL carrier, the WTRU may selectthe UL carrier with the smallest Pmax 1518. Having selected the ULcarrier, the WTRU may select the preamble group chosen in the precedingsteps 1520. The WTRU may then randomly select a RA preamble within theselected preamble group 1522.

A random access retransmission may include retransmitting an UL messagecontaining the C-RNTI MAC control element or the UL message includingthe common control channel (CCCH) service data unit (SDU). The samerandom access preamble group (A or B) as was chosen for the earlierpreamble transmission attempt may be selected. For the retransmission,the preamble may be sent on a different UL carrier. The UL carrier maybe chosen as in element 1514, element 1516, or element 1518. A randomaccess preamble may be randomly selected within the selected preamblegroup.

FIG. 16 shows an example procedure 1600 of initial RA transmission. TheWTRU may select one UL carrier among UL CCs available for RA 1604. TheUL carrier may be selected in one of a plurality of ways. The WTRU mayrandomly select one UL carrier within the carrier set 1606.Alternatively, the WTRU may select the UL carrier with the smallest pathloss within the carrier set 1608. Alternatively, if Pmax is assigned perUL carrier, the WTRU may select the UL carrier with the smallest Pmax.Alternatively, if there are different RACH parameters for each ULcarrier, the WTRU may select the UL carrier that provides the highestprobability of accessing the carrier 1612. In another alternative, theWTRU may select the UL carrier that provides a suitable probability ofaccessing the carrier. For example, the probability may be a function ofat least one of: (1) whether or not previous attempts were successfulfor a given UL CC/PRACH resource; (2) the number of preambleretransmissions for a given UL CC/PRACH resource; (3) the presence of RApreambles group B for a given UL CC/PRACH resource; or (4) the availabletransmit power based on Pmax and the path loss of the associated DL CC.

The selection criteria for element 1612 may include (1) the access classprobability factor that allows the highest probability of random accesssuccess or that provides a suitable probability of accessing thecarrier; (2) the UL carrier that allows a greater number of hybridautomatic repeat request (HARQ) msg3 transmissions; (3) the UL carrierthat allows a greater offset between preamble and msg3; (4) the ULcarrier that allows a highest Pmax, such that the WTRU may have agreater chance of succeeding and selecting RA preambles from group B; or(5) other parameters such as, for example, a delta preamble that mayallow the WTRU to select RA preambles from a particular group.

Upon selecting the UL carrier, the WTRU may determine whether RApreambles group B criteria are met 1614. If RA preambles group Bcriteria are not met, the WTRU may select RA preambles group A 1616. Ona condition that RA preambles group B criteria are met, the WTRU mayselect RA preambles group B 1618. The WTRU may then randomly select a RApreamble within the selected group 1620.

A random access retransmission may include retransmitting an UL messagecontaining the C-RNTI MAC control element or the UL message includingthe CCCH SDU. The WTRU may select the same UL carrier that was used forthe first preamble transmission. Within the same UL carrier, the samerandom access preamble group (A or B) as was chosen for the earlierpreamble transmission attempt may be selected. A random access preamblemay be randomly selected within the selected preamble group.

Alternatively or additionally, a WTRU may perform a retransmission byrandomly selecting one UL carrier within the same carrier set used forthe preamble transmission attempt corresponding to the firsttransmission. Within the selected UL carrier, the same random accesspreamble group (A or B) as was chosen for the earlier preambletransmission attempt may be selected. A random access preamble may berandomly selected within the selected preamble group.

Alternatively or additionally, a WTRU may perform a retransmission byrandomly selecting an UL carrier. Within the selected UL carrier, arandom access preamble group may be selected according to element 1614,element 1616, or element 1618. A random access preamble may be randomlyselected within the selected preamble group.

Alternatively or additionally, a WTRU may perform a retransmission byselecting a UL carrier in the same manner as in the initial selection.Depending on the conditions, a different UL carrier than the UL carrierselected for initial transmission may be selected.

FIG. 17 shows an example of a procedure 1700 for transmitting a RARcorresponding to a WTRU's preamble transmission. A RAR corresponding toa WTRU's preamble transmission on a given UL carrier 1704 may betransmitted on a known DL PCC 1706 or transmitted on the DL carrierpaired with the given UL carrier 1714. If the RAR is transmitted on aknown DL PCC carrier 1706 and RAR windows across different UL carriersmay not overlap 1708, RAR windows (for example, ResponseWindowSize) maybe configured small enough so that RAR windows associated with differentUL carriers do not overlap 1710. This may be demonstrated asra-ResponseWindowSize≦reduced_RACH_period (for example,T_(RACH)/N_(UL)). Thus, the RA-RNTI computation in LTE-A may be kept thesame as in LTE , such that:

RA-RNTI=1+t_id+10*f_id   (Equation 2)

where t_id may be the index of the first subframe of the specified PRACH(0≦t_id<10) and f_id may be the index of the specified PRACH within thatsubframe, in ascending order of frequency domain (0≦f_id<6).

Alternatively, if the RAR is transmitted on a known DL PCC 1706 and RARwindows on different UL carriers may overlap 1708, the RA-RNTIassociated with the PRACH in which the RA preamble is transmitted may becomputed as a function of t_id, f_id, and carrier_id 1712, such that:

RA-RNTI=f(t_id, f_id, carrier_id)   (Equation 3)

where carrier_id is the index of the UL carrier on which a RA preambleis transmitted and whose RAR is mapped on the DL PCC (1<carrier_id≦N).An example of function f( ) may be given as:

RA-RNTI=f(t_id, f_id, carrier_id)=1+carrier_id*(t_id+10*f_id)  (Equation 4)

In this formula, the carrier_id of the UL carrier that is paired withthe DL PCC, as signaled in SIB2, should be equal to 1. Thus, backwardcompatibility with other WTRUs may be maintained because RA-RNTI is1+t_id+10*f_id. Another example of function f( ) may be given as:

RA-RNTI=f(t_id, f_id, carrier_id)=(carrier_id-1)*(t_id+10*f_id)  (Equation 5)

In another embodiment, the RAR corresponding to the WTRU's preambletransmission may be transmitted on the DL carrier paired with the givenUL carrier 1714. In this embodiment, the RA-RNTI computation may beperformed in the same manner as in LTE Release 8 1716.

Table 1 shows an example of RNTI values. Allocation of RNTI values mayincrease the range for RA-RNTI. For example, Value1 _(FDD) may equal(N_(max)*10)−1 and Value1 _(TDD) may equal (N_(max)*60)−1, where N_(max)may be the maximum number of UL CCs whose RARs are mapped on the same DLcarrier.

TABLE 1 Value (hexa-decimal) FDD TDD RNTI 0000-Value1_(FDD)0000-Value1_(TDD) RA-RNTI Value1_(FDD) + 1 − Value1_(TDD) + 1 − C-RNTI,Semi-Persistent Value2 Value2 Scheduling C-RNTI, Temporary C-RNTI,Transmit Power Control (TPC)-PUCCH- RNTI and TPC-PUSCH-RNTI Value2 + 1 −FFFD Reserved for future use FFFE Paging (P)-RNTI FFFF SystemInformation (SI)-RNTI

RACH delay may be reduced via joint processing of the RACH request whileemploying carrier aggregation in wireless communications. The eNB maydetect a RA preamble on one UL carrier. The eNB may schedule RACH msg3transmission on any one of the N_(UL) UL carriers. A WTRU may follow thegrant received in the RAR, which may provide PUSCH resources on adifferent UL than the preamble was sent on.

FIG. 18 shows an overview of joint processing of a RACH request at aneNB, including a scheduler 1802 and multiple component carriers 1804_(a)-1804 _(n). Each component carrier 1804 _(a)-1804 _(n) may include aRLC layer 1806 _(a)-1806 _(n), a MAC layer 1808 _(a)-1808 _(n), and aPHY layer 1808 _(a)-1808 _(n). When a WTRU request is received at thescheduler 1802, the eNB may respond to the request by considering thecapacity of all component carriers 1804 _(a)-1804 _(n) rather thanconsidering only the resource availability of the CC that initiated theRA procedure. Upon detection of a first RACH preamble received on any ULCC 1804 _(a)-1804 _(n), the eNB may check the resource usage status andload of all available UL CCs 1804 _(a)-1804 _(n). The eNB may thenrespond to the WTRU's RA preamble (for example, a request for PUSCHallocation for a RACH msg3) by scheduling PUSCH on any available UL CC1804 _(a)-1804 _(n).

In this manner, the assigned UL CC 1804 _(a)-1804 _(n) may or may not bethe same as the CC 1804 _(a)-1804 _(n) that the WTRU transmitted itsRACH transmission on.

FIG. 19 shows an example of a procedure 1900 for determining which DLcarrier the RAR may be received on. A WTRU may need to determine whichDL carrier(s) the RAR may be received on 1904 and may do so, forexample, according to one or a combination of the following embodiments.In one embodiment, a WTRU may monitor for PDCCH candidates in the commonsearch space on a single DL carrier 1906, assuming that PDCCH is definedon a per-carrier basis. The DL carrier may be a function of the ULcarrier used for preamble transmission. Alternatively, the DL carriermay be a function of the preamble that was transmitted. For example, theDL carrier may depend on which preamble group the transmitted preamblebelongs to. Alternatively, the DL carrier may be a function of acombination of the two previous alternatives, based on both the ULcarrier used for preamble transmission and the transmitted preamble. ThePDCCH may be received from a PCC indicated from system information, orit may be received on the same DL carrier on which the data part is tobe received. Alternatively, the WTRU may monitor for PDCCH candidates inthe common search space of the WTRU-specific PCC while in connectedmode. The WTRU-specific PCC may be assigned by the network in a RRCmessage upon the WTRU entering Connected mode.

In another embodiment, a WTRU may monitor a plurality of PDCCHcandidates in the common search space, each corresponding to a single DLcarrier 1908, assuming that PDCCH is defined on a per-carrier basis. TheDL carriers may be a function of the UL carrier used for preambletransmission. Alternatively, the DL carriers may be a function of thetransmitted preamble. For example, the DL carriers may depend on whichpreamble group the transmitted preamble belongs to. Alternatively, theDL carriers may be a function of a combination of the two previousalternatives, based on both the UL carrier used for preambletransmission and the transmitted preamble. The PDCCHs may be received ona PCC indicated from system information, or they may be received on therespective DL carriers on which the data part is to be received.

In another embodiment, the WTRU may monitor a single PDCCH for data onany of the DL carriers 1910. The PDCCH may be received on a PCCindicated from system information, or it may be received on a DL carrierthat is a function of either the UL carrier used for preambletransmission, the transmitted preamble, or a combination of both. The DLcarrier on which the data part (PDSCH) is received may also be afunction of either the UL carrier used for preamble transmission, thetransmitted preamble, or a combination of both. Alternatively, the DLcarrier on which the data part is to be received may be indicated by thecontents of the PDCCH or by the RA-RNTI used to mask the PDCCH.

The monitoring described in the above embodiments (element 1906 throughelement 1910), may also include a WTRU detecting a RAR identified by oneRA-RNTI value or by one of a set of RA-RNTI values 1912. The one RA-RNTIvalue or the set of RA-RNTI values may be determined from a combinationof the t_id and f_id parameters plus one or a combination of the ULcarriers used for preamble transmission, the DL carrier used for PDCCHtransmission of the RAR, and/or the DL carrier used for PDSCHtransmission of the RAR.

FIG. 20 shows an example of a procedure 2000 for preambleretransmission. A WTRU may determine that a RAR failure has occurred andmay select one or a plurality of UL carriers to be used forretransmission of the RA preamble. If a WTRU determines that a RARfailure has occurred and the number of UL carriers is greater than 12004, the WTRU may then determine whether a PDCCH matching the RA-RNTIwas received 2006.

If no PDCCH matching the RA-RNTI was received 2006 during the RA windowinterval, the WTRU may then select one or a plurality of UL carriers forretransmission of the RA preamble according to one or a combination ofthe following embodiments. In one embodiment, the WTRU may send the RApreamble on another UL carrier after a backoff period 2008. Optionally,the WTRU may select the UL carrier randomly 2010. During randomselection of the UL carrier, the WTRU may exclude the unsuccessfulcarrier from the potential carriers 2012 or include the unsuccessfulcarrier in the potential carriers 2014. Optionally, the power rampscheme used for the RA preamble may be implemented as well.Alternatively, the WTRU may use any of the alternatives described aboveregarding PRACH resource selection.

In another embodiment, UL carriers may be ranked based on a path lossmeasurement 2016 as described above. The WTRU may send the firstretransmission on the second highest ranking UL carrier 2018. Thisprocess may be repeated and the WTRU may send the second retransmissionon the third highest ranking UL carrier, and so on. Optionally, after apredetermined number of RA preamble retransmissions, the WTRU mayre-select the highest ranking UL carrier 2020.

In another embodiment, the WTRU may retransmit on the same UL carrierfor a predetermined number of transmissions before selecting a new ULcarrier 2022.

In another embodiment, the WTRU may randomly decide whether to select anew UL carrier 2024. Optionally, the WTRU may assign a probability (lessthan 1) that a new UL carrier is selected 2026.

If a PDCCH matching the RA-RNTI was received 2006, the WTRU maydetermine whether the PDCCH contains a backoff indicator or whether theRAR is missing a preamble identifier 2030. If the PDCCH contains abackoff indicator or the RAR is missing a preamble identifier, the WTRUmay select a UL carrier according to the embodiments described above(element 2008 through element 2026) or the WTRU may follow a modified ULcarrier algorithm 2032. An example of a modified UL carrier algorithmmay be using the last digit of the WTRU's IMSI, the SFN, and thesubframe ID to decide whether the WTRU should reselect a new UL carrierfor the RA preambles 2034.

Once a WTRU has detected a RAR on one of the DL carriers, the WTRU maythen select an UL carrier on which the next message (for example, msg3)may be transmitted. In one embodiment, the WTRU may transmit the nextmessage on the same UL carrier that is used for preamble transmission.In another embodiment, the UL carrier (and optionally a transmit poweradjustment) may be determined based on the contents of the RAR that wasreceived. In another embodiment, the UL carrier may be determined basedon the DL carrier of the PDCCH used for the RAR scheduling. In anotherembodiment, the UL carrier may be determined based on the DL carrierfrom which the data part (for example, PDSCH) of the RAR was received.

The WTRU may then determine the DL carrier over which the next message(for example, msg4) may be received. In one embodiment, the DL carriermay be determined as the same DL carrier(s) of the PDCCH used for RARscheduling. In another embodiment, the DL carrier may be determined asthe same DL carrier(s) of the PDSCH used for RAR reception. In anotherembodiment, each of the previous two embodiments may be used,determining the DL carrier based on the DL carrier(s) of the PDCCH usedfor RAR scheduling as well as the DL carrier(s) of the PDSCH used forRAR reception. In another embodiment, the DL carrier may be determinedbased on the contents of the RAR.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. An eNodeB comprising: a processor; a transmitteroperably coupled to the processor, the transmitter and processorconfigured to transmit downlink control information (DCI); and areceiver operably coupled to the processor, the receiver and processorconfigured to receive, from a wireless transmit receive unit (WTRU), arandom access preamble on a secondary uplink component carrier selectedfrom a plurality of component carriers; wherein the transmitter andprocessor are further configured to transmit a random access response(RAR), to the WTRU, always on a primary downlink component carrier inresponse to the random access preamble; and wherein the transmitter andprocessor are further configured to transmit downlink transmissions viathe primary downlink component carrier and one or more secondarycomponent carriers.
 2. The eNodeB of claim 1, wherein a physicaldownlink control channel (PDCCH) order is transmitted in the DCI,wherein the DCI is DCI format 1a.
 3. The eNodeB of claim 2, wherein thePDCCH order includes a carrier indicator field (CIF).
 4. The eNodeB ofclaim 2, wherein the DCI format 1a includes a preamble index and therandom access preamble is received from the WTRU in accordance with thepreamble index.
 5. The eNodeB of claim 4, wherein the transmitter andprocessor are further configured to transmit the preamble index with avalue “000000” to cause a random selection of the preamble.
 6. TheeNodeB of claim 1, wherein the transmitter and processor are furtherconfigured to transmit random access channel configuration informationfor two or more component carriers.
 7. The eNodeB of claim 1, whereinthe DCI is transmitted via a first component carrier associated with afirst cell and wherein the secondary uplink component carrier isassociated with a second cell.
 8. The eNodeB of claim 1, wherein the RARincludes a timing advance.
 9. The eNodeB of claim 8, wherein theprocessor and receiver are further configured to receive an uplinktransmission from the WTRU adjusted by the timing advance.
 10. TheeNodeB of claim 9, wherein the processor and receiver are furtherconfigured to receive a physical uplink shared channel (PUSCH)transmission from the WTRU adjusted by the timing advance.
 11. A methodperformed by an eNodeB, the method comprising: transmitting downlinkcontrol information (DCI); receiving, from a wireless transmit receiveunit (WTRU), a random access preamble on a secondary uplink componentcarrier selected from a plurality of component carriers; transmitting arandom access response (RAR), to the WTRU, always on a primary downlinkcomponent carrier in response to the random access preamble; andtransmitting downlink transmissions via the primary downlink componentcarrier and one or more secondary component carriers.
 12. The method ofclaim 11, wherein a physical downlink control channel (PDCCH) order isreceived in the DCI, wherein the DCI is DCI format 1a.
 13. The method ofclaim 12, wherein the PDCCH order includes a carrier indicator field(CIF).
 14. The method of claim 12, wherein the DCI format 1a includes apreamble index and the random access preamble is received from the WTRUin accordance with the preamble index.
 15. The method of claim 14,further comprising transmitting the preamble index with a value “000000”to cause a random selection of the preamble.
 16. The method of claim 11,further comprising transmitting random access channel configurationinformation for two or more component carriers.
 17. The method of claim11, wherein the transmitting the DCI includes transmitting the DCI via afirst component carrier associated with a first cell, and wherein thesecondary uplink component carrier is associated with a second cell. 18.The method of claim 11, wherein the RAR includes a timing advance. 19.The method of claim 18, further comprising receiving an uplinktransmission from the WTRU adjusted by the timing advance.
 20. Themethod of claim 19, wherein the receiving the uplink transmissionincludes receiving a physical uplink shared channel (PUSCH) transmissionfrom the WTRU adjusted by the timing advance.